Field of the Invention
The present invention relates to an imaging device.
Description of the Related Art
Imaging devices such as complementary metal oxide semiconductor (CMOS) image sensors include a pixel circuit region, in which pixel circuits are disposed, and a peripheral circuit region, in which peripheral circuits are disposed. In the pixel circuit region, the sensitivity can be improved with light guide portions serving as optical waveguides provided on photoelectric conversion portions.
These light guide portions can be formed as follows: Initially, holes are formed in portions of an insulating layer provided in the pixel circuit region at positions above the photoelectric conversion portions. Next, the holes are filled with a dielectric material. In addition, the surface of the excess dielectric material remaining outside the holes is subjected to a planarization process so that the excess dielectric material is removed. Members formed of the dielectric material remaining in the holes (dielectric members) serve as the light guide portions.
When the holes have been filled with the dielectric material, in the peripheral circuit region where the holes are not formed, the dielectric material with which the holes are not filled remains on the insulating film. Thus, the level of the surface of the dielectric material varies between the peripheral circuit region and the pixel circuit region. Furthermore, when the planarization process is performed on the dielectric material, the level of the dielectric material varies between a central portion and a peripheral portion of the pixel circuit region. The variation of the level of the surface of the dielectric members between the central portion and the peripheral portion of the pixel circuit region leads to variation of signal output between the central portion and the peripheral portion of the pixel circuit region. This causes degradation of the quality of images.
A technique, in which a dummy opening portion is provided in an insulating layer in a region at the periphery of an effective pixel region, is described in Japanese Patent Laid-Open No. 2009-164247. Examples of the region at the periphery of the effective pixel region include an optical black region and a peripheral circuit region.
The difference in the film thickness produced at a boundary region between the effective pixel circuit region and its peripheral circuit region is not sufficiently reduced only with the dummy opening portion provided in the optical black region. Furthermore, since transistors and wiring are densely disposed in a peripheral circuit region, an area in which the dummy opening portion can be formed is limited.